1. Field of the Invention
The present invention relates to a control method of a robot apparatus including a hand that can flexibly touch an object and to the robot apparatus. The present invention can be applied to a working robot and a legged mobile robot.
2. Description of the Related Art
In a control method of a manipulator, it is becoming more important that a hand be able to flexibly touch an object. If the method is applied to an industrial robot, cooperative work of a robot apparatus and a human can be realized, and fitting work of components is facilitated by controlling the direction of the flexibility of the hand. If the method is applied to a legged mobile robot, impact on the body can be alleviated by soft landing, and absorption of a difference in level allows stable walking on an unleveled land.
To realize the control of the flexibility of the hand, impedance control for installing a force sensor on the hand or control using artificial muscle actuators is performed. Muscles of a human are known to serve as actuators, and at the same time, serve as a viscoelasticity-variable control mechanism. Among the artificial muscles, pneumatic rubber artificial muscles represented by McKibben artificial muscles particularly have similar viscoelasticity characteristics as those of the human muscles. Therefore, the control of the softness of artificial muscle actuators arranged on a manipulator allows touching an object at arbitrary flexibility of hand. However, the artificial muscle actuators are known to have difficulties in controllability for reasons that the viscoelasticity characteristics indicate non-linearity and that the actuators need to be antagonistically arranged and controlled because the force is generated only in a contraction direction.
Regarding this, disclosed is a technique for generating feedforward input for simultaneous control of a joint angle and flexibility of hand using a model of a manipulator with viscoelasticity characteristics of muscles and using a corrected value calculation unit (see Japanese Patent No. 3436320). In Japanese Patent No. 3436320, the model is used to output a joint angle and viscoelasticity coefficients of artificial muscle actuators at the time of control input, and the joint angle and a target value are compared. An error between the joint angle and the target value is back-propagated to the corrected value calculation unit to correct the feedforward input. Operation of providing the corrected feedforward input again to the model is repeated to gradually obtain the feedforward input.
In Japanese Patent No. 3436320, the joint angle and the flexibility of hand are simultaneously controlled by the feedforward control. However, there is no study example for antagonistically driving the artificial muscle actuators by minimum control input. To minimize the control input, hand flexibility corresponding to a target trajectory of the joint angle needs to be taken into account to simultaneously optimize the hand flexibility and the control input. However, the target stiffness of the hand flexibility is provided in advance in the feedforward control of Japanese Patent No. 3436320, and an algorithm for optimizing the hand flexibility is not included.
An object of the present invention is to simultaneously optimize a torque command value and a joint stiffness command value in trajectory control of a joint angle to antagonistically drive links based on minimum driving force command values.